The present invention relates generally to a networked motorized drive roller conveyor.
Conventional conveyor control systems utilize a central Programmable Logic Controller (“PLC”) mounted in a central control panel. This type of system requires control devices, e.g., photo-eyes, solenoid valves, and motor starters, to be terminated at the main control panel. A typical control system utilizing a PLC requires several hundred to several thousand feet of control wiring, which requires significant time, labor and money to route and terminate the wiring. In addition, the PLC requires specialized knowledge, e.g., knowledge of ladder logic, and familiarity with the many different interface requirements unique to each manufacturer's product. Moreover, since there is a central controller, response time with respect to the control devices may be increased because the single processor must account for all operations occurring within the system.
A Motorized Drive Roller (“MDR”) is a conveyor roller with an integrated motor. An MDR is typically configured to drive a plurality of idler rollers, usually by way of urethane belts or chains. The MDR and idler rollers thus define a zone. There is typically one MDR per zone.
For conveyor systems that utilize MDR technology, networked motor controllers are frequently used to handle basic transport, diversion, and accumulation tasks to move items through a conveyor system. These motor controllers are mounted in close proximity to the MDR rollers and directly interface with the product sensors associated with each MDR. An MDR conveyor system has many advantages over other conveyor technologies, such as lower power consumption, noise reduction, and a decreased need for maintenance.
Unlike conventional control systems, modular distributed controls don't require hundreds to thousands of feet of wiring from a centralized PLC to each device in the system. With controls located near the control devices, wiring and wiring labor may be reduced. This shortens the time to complete implementation and provides a parallel control capability that minimizes response time issues common to conventional PLC based systems. Because the system is not limited by the speed of a central processor in a PLC, the system can grow without worry of overtaxing a centralized controller. Testing and start-up time is also reduced, as various segments of the system can be installed and tested independent of other segments.
It is common practice in existing conveyor systems that use MDR roller conveyor along with associated motor controllers to utilize smaller, localized PLC's distributed throughout the system to handle conveyor operations such as diverting, bar code scanning, RFID communication, label applications, etc. These peripherals typically communicate serially (RS232 or RS485) or via a network protocol such as Ethernet. Having multiple PLCs in this environment creates other undesirable issues as single point diagnostics are difficult to implement.
The networked, distributed control system of the present invention provides localized controls for various operations, e.g., diverting, bar code scanning, RFID transactions, labeling, etc. The inventive control system can also handle the basic MDR conveyor drive and accumulation responsibilities, which greatly reduces the wiring needed for the system, implementation time, and cost while maintaining a centralized diagnostic capability. Additional capability to allow localized programming as well as status and diagnostics capability are additional benefits of the inventive control system. Eliminating the need for PLCs and associated ladder logic is a further benefit of the inventive design because it reduces the complexity of installation, operation and modification of the control system and corresponding conveyor system.
As noted above, MDR conveyor systems have many advantages over other conveyor technologies, such as lower power consumption, noise reduction, and less maintenance. However, prior to the present invention, MDR systems lacked the ability to control the size of gaps between items on the conveyor system. Prior art systems are also limited to transporting “Items” that are shorter in length than a single “Zone”.
Existing technology is typically marketed as “Zero pressure Accumulation” conveyor technology, as items on the conveyor are allowed to accumulate with one item per zone. As such, with control technology currently marketed, items accumulate with varying gaps between items, based on the length of the items.
In accordance with one aspect of the inventive conveyor control system, a gap control arrangement is used to control gaps between items on the conveyor system. The elimination of gaps between items on the conveyor system is desirable, in that gaps reduce the number of items that can be accumulated on the conveyor, providing lower accumulation efficiency. Thus, reducing or even eliminating gaps between items helps to maximize the accumulation efficiency of the conveyor system. The gap control system incorporates the use of MDR technology and its desirable attributes while at the same time providing the operator with the ability to control the size of the gaps between items on the conveyor system.
In one embodiment of the invention, a networked motorized drive roller conveyor includes a plurality of motorized drive roller assemblies, where each assembly comprises a zone. The conveyor has a plurality of networked cards, with each card controlling a pair of adjacent zones. The conveyor further has a plurality of sensors for detecting items on the conveyor, with each sensor corresponding to a zone. For a pair of adjacent zones, the corresponding networked card measures a gap between consecutive items on the conveyor by beginning a counter when a trailing edge of a first item passes the sensor of an upstream zone within the pair of zones, and stopping the counter when a leading edge of the second item passes the sensor of the upstream zone within the pair of zones, to generate a counter value. If the first item is stopped in the downstream zone, the networked card causes the motorized drive roller assembly of the upstream zone to move the item into the downstream zone a distance derived from the counter value before stopping the movement of the second item.
In another embodiment of the invention, a motorized drive roller conveyor includes an upstream zone and a downstream zone. Each zone has a drive roller, an idler roller that is driven by the drive roller, and a sensor. A card controls the upstream zone and the downstream zone. The card measures a gap between a first item on the conveyor and a second item on the conveyor by beginning a counter when a trailing edge of the first item passes the sensor of the upstream zone and stopping the counter when a leading edge of the second item passes the sensor of the upstream zone to generate a counter value. If the first item is stopped in the downstream zone, the card of the upstream zone causes the drive roller of the upstream zone to advance the second item into the downstream zone for a distance derived from the counter value before stopping the movement of the second item.
In yet another embodiment of the invention, a method for controlling a gap between items on a motorized drive roller conveyor includes the steps of: (a) detecting a trailing edge of a first item at a predetermined location in a first zone on a conveyor system; (b) beginning a counter once the trailing edge of the first item passes the predetermined location; (c) stopping the counter upon the first occurrence of the following:(i) a leading edge of a second item is detected at the predetermined location, or (ii) the first item is stopped in a downstream zone adjacent the first zone; and (d) generating a counter value.
These and other aspects and advantages of the present invention will be made apparent from the following description taken together with the drawings.